U.S. patent number 8,427,726 [Application Number 13/257,546] was granted by the patent office on 2013-04-23 for hollow reflecting optical element and scanning optical device.
This patent grant is currently assigned to Konica Minolta Opto, Inc.. The grantee listed for this patent is Shinichiro Hara, Naoki Kaneko, Hiroshi Takagi. Invention is credited to Shinichiro Hara, Naoki Kaneko, Hiroshi Takagi.
United States Patent |
8,427,726 |
Hara , et al. |
April 23, 2013 |
Hollow reflecting optical element and scanning optical device
Abstract
Provided are a resinous reflecting optical element that achieves
high mirror surface precision by mitigating the warping effects
associated with contraction during resin hardening and suppressing
the distortion of a mirror surface that results from resistance to
mold release, and a scanning optical device that uses said
reflecting optical element. The reflecting optical element is
characterized by having a long, tabular substrate (3), a mirror
surface section (2) positioned on one surface of the substrate (3),
and a hollow portion (4) positioned within the interior of the
substrate (3), and is also characterized in that, as a result of
configuring so that the hollow portion (4) is longer than the
mirror surface section (2), warping and sink marks which form due
to contraction during resin hardening are mitigated across the
entire mirror surface section (2), and in that the entire mirror
surface section (2) protrudes above the surface of the substrate
(3), thereby suppressing the increase in resistance to mold release
that occurs when a metallic mold is gripped by the molding during
resin contraction, and preventing distortion of the mirror surface
section (2) that is caused by resistance to mold release.
Inventors: |
Hara; Shinichiro (Hachioji,
JP), Kaneko; Naoki (Hachioji, JP), Takagi;
Hiroshi (Hachioji, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Hara; Shinichiro
Kaneko; Naoki
Takagi; Hiroshi |
Hachioji
Hachioji
Hachioji |
N/A
N/A
N/A |
JP
JP
JP |
|
|
Assignee: |
Konica Minolta Opto, Inc.
(Tokyo, JP)
|
Family
ID: |
42739511 |
Appl.
No.: |
13/257,546 |
Filed: |
February 4, 2010 |
PCT
Filed: |
February 04, 2010 |
PCT No.: |
PCT/JP2010/051603 |
371(c)(1),(2),(4) Date: |
September 19, 2011 |
PCT
Pub. No.: |
WO2010/106845 |
PCT
Pub. Date: |
September 23, 2010 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20120008184 A1 |
Jan 12, 2012 |
|
Foreign Application Priority Data
|
|
|
|
|
Mar 19, 2009 [JP] |
|
|
2009-067960 |
|
Current U.S.
Class: |
359/208.1;
359/848; 359/216.1 |
Current CPC
Class: |
B41J
2/471 (20130101); B29D 11/00596 (20130101); G02B
26/126 (20130101); G02B 27/0031 (20130101); B29C
45/7613 (20130101); B29C 2945/76257 (20130101); B29C
2945/76381 (20130101); B29C 2945/76585 (20130101); B29C
45/1704 (20130101); B29C 45/762 (20130101); B29C
2945/76454 (20130101); B29C 2945/76167 (20130101); B29C
2945/76474 (20130101); B29L 2011/0058 (20130101); B29C
2945/76943 (20130101); B29C 2945/76488 (20130101); B29C
2945/76397 (20130101) |
Current International
Class: |
G02B
26/08 (20060101) |
Field of
Search: |
;359/216.1-219.2,205.1,207.1-207.5,208.1,848,868-869,871 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
6-175006 |
|
Jun 1994 |
|
JP |
|
2001-105449 |
|
Apr 2001 |
|
JP |
|
2001-124912 |
|
May 2001 |
|
JP |
|
2001-188113 |
|
Jul 2001 |
|
JP |
|
2002-277803 |
|
Sep 2002 |
|
JP |
|
2003-262816 |
|
Sep 2003 |
|
JP |
|
2004/025789 |
|
Jan 2004 |
|
JP |
|
2004-170607 |
|
Jun 2004 |
|
JP |
|
Primary Examiner: Phan; James
Attorney, Agent or Firm: O'Connor; Cozen
Claims
The invention claimed is:
1. A reflecting optical element comprising: a long tabular
resin-made substrate having a hollow portion; and a mirror surface
section located at part of a surface of the substrate, wherein the
hollow portion is located inside the substrate with the mirror
surface section formed thereon, and is longer than a distance from
a center of the mirror surface section to both ends of the mirror
surface section in a direction of length, and the mirror surface
section is a reflecting optical element wherein the entire mirror
surface section protrudes above the surface of the substrate.
2. The reflecting optical element of claim 1, wherein the hollow
portion is further longer than the distance from the center of the
mirror surface section to both ends of the mirror surface section
in a direction of width.
3. The reflecting optical element of claim 1, wherein the
reflecting optical element reflects a light emitted from a light
source during an operation of scanning along the surface of the
mirror surface section in the direction of length.
4. The reflecting optical element of claim 1, wherein a surface
roughness Ra on a surface of the substrate with the mirror surface
section of the reflecting optical element formed thereon is
preferably formed within a range of Ra.ltoreq.5 (nm).
5. A scanning optical device comprising: a light source; a polygon
mirror; a converging unit for inputting a light emitted from the
light source and converging the light onto the polygon mirror; and
a reflecting optical element for providing f.theta. characteristic
to the light scanned by rotation of the polygon mirror at a
prescribed speed, wherein the reflecting optical element comprises:
a long tabular resin-made substrate having a hollow portion; and a
mirror surface section located at part of a surface of the
substrate, wherein the hollow portion is located inside the
substrate with the mirror surface section formed thereon, and is
longer than a distance from a center of the mirror surface section
to both ends of the mirror surface section in a direction of
length, and the mirror surface section is a reflecting optical
element wherein the entire mirror surface section protrudes above
the surface of the substrate.
6. The scanning optical device of claim 5, wherein the hollow
portion is further longer than the distance from the center of the
mirror surface section to both ends of the mirror surface section
in a direction of width.
7. The scanning optical device of claim 5, wherein a surface
roughness Ra on a surface of the substrate with the mirror surface
section of the reflecting optical element formed thereon is
preferably formed within a range of Ra.ltoreq.5 (nm).
8. The scanning optical device of claim 5, wherein a wavelength of
the light emitted from the light source is 500 nm or less.
Description
RELATED APPLICATIONS
This application is a U.S. National Phase Application under 35 USC
371 of International Application PCT/JP2010/051603 filed Feb. 4,
2010.
This application claims the priority of Japanese application No.
2009-067960 filed Mar. 13, 2009, the entire content of which is
hereby incorporated by reference.
FIELD OF THE INVENTION
The present invention relates to a reflecting optical element
constituting an optical system used in a scanning optical device
and image forming device, particularly to a resin-made reflecting
optical element having a hollow portion formed in the element.
BACKGROUND OF THE INVENTION
In a conventional image forming apparatus such as a copying machine
or printer, the laser scanning optical device for forming an
electrostatic latent image on a photoreceptor has often used a
long-sized optical element as an optical element for providing the
f.theta. characteristic (a characteristic for ensuring that an
optical beam deflected by a polygon mirror or the like is scanned
on a surface to be scanned at a equidistant speed), for example. In
such an optical element, a prescribed warping is kept with a high
accuracy particularly in the scanning direction so that the optical
path of the laser beam is adjusted; for example, the main scanning
speed is adjusted when the laser beam passes through the optical
element or is reflected by the same.
The aforementioned optical element made of glass, metal or ceramics
is widely known. In recent years, a resin-made optical element has
come to be employed in view of molding ease, greater freedom of
designing, and reduced costs.
In the meantime, as a laser beam, the attention of the industry is
focused on a short-wave light source having a wavelength of 500 nm
or less, particularly in the vicinity of 400 nm in recent years
because it provides high definition image recording, enhanced
recording density, longer-service life and stable output. There is
a need to use a resin-made optical element as a means for adjusting
the optical path of the light emitted from this light source.
When the scanning optical device for adjusting the optical path of
laser beam by means of a transparent type refraction optical
element disclosed in the Patent Literature 1, namely, a transparent
lens, is structured in such a way that the laser beam from the
short-wave light source is used as the laser beam and a resin-made
lens is used as the transparent lens for adjusting the optical path
of laser beam, a short-wave laser beam will pass through the resin,
and weatherability of the resin-made lens comes into question.
To solve the problem of weatherability, the present inventor
considered use of a mirror for reflecting the laser beam, namely, a
reflecting optical element as a means of adjusting the laser beam
optical path, without using a transparent lens, namely, a
transparent refraction type optical element that allows laser beam
to pass through.
This is because of the following reason: A transparent optical
element requires countermeasures to be provided to ensure
weatherability, including the interior of the lens wherein light
passes through. By contrast, the reflecting lens surface requires
such countermeasures to be taken only for the reflecting optical
element. This is a great advantage.
However, the following new problem arises in this case: When a
reflecting optical element is used to adjust the optical path of
the laser beam, the surface precision required for the profile of
the reflecting optical surface is about four times that required
for the transparent lens. This is because of the following reasons:
In the case of the transparent lens, the entrance and exit surfaces
of the lens are used to adjust the optical path of the laser beam
and beam profile. By contrast, in the case of a reflecting optical
element, the optical path of the laser beam and beam profile are
adjusted by one reflecting surface.
In the optical element wherein the profile of the optical surface
is required to ensure a high degree of surface precision,
particularly in the optical element for adjusting the main scanning
speed of the laser beam, there will be an increased impact on the
deformation of the optical surface given by the warping or sink
marks resulting from contraction during resin hardening, and on the
warping produced in the direction of length, i.e., in the scanning
direction, making it difficult to perform molding with such a high
degree of surface precision maintained, even if the conventional
injection molding procedure is utilized.
To solve this problem, the present inventors paid attention to the
effect of the hollow injection molding, and considered application
of hollow injection molding to the optical components. Tensile
stress during resin contraction that may cause warping and sink
marks of the molded products is released to the hollow portion by
hollow molding according to hollow injection molding process. Then
a sink marks appears on the surface of the hollow portion, thereby
suppressing the warping and sink marks occurring on the surface of
the hollow portion. This enhances surface precision, i.e., the
mirror surface precision in the reflecting optical element.
The hollow injection molding technique is disclosed in Patent
Literature 2. According to this technique, the hollow portion is
designed wider than the mirror surface section of the reflecting
optical element to achieve the effect of formation of a hollow
portion over the entire mirror surface section. This technique will
be advantageous in the sense the tensile stress during resin
contraction is released to a certain extent by formation of a
hollow portion over the entire mirror surface section.
However, this conventional technique has been found to be
insufficient to maintain the surface precision required of the
aforementioned reflecting optical element, particularly the
reflecting optical element employed in the scanning optical device
using the short-wave light source.
BACKGROUND ART DOCUMENT
Patent Literature
Patent Literature 1: Japanese Unexamined Patent Application
Publication No. 2003-262816 Patent Literature 2: Japanese
Unexamined Patent Application Publication No. 2001-124912
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
In the reflecting optical element disclosed in the Patent
Literature 2, it has been found out that a serious distortion
occurs to the periphery of a mirror surface section at the time of
mold release in the molding operation. This is because of the
following reasons: The mirror surface section is form in a concave
in such a way as to be gripped inside the substrate, namely, the
periphery of the substrate is protruding. Accordingly, the resin
molded article (reflecting optical element) contracts during resin
hardening and the mold on the periphery of the mirror surface
section is gripped by the protrusion of the mirror surface section
in the resin molded article (reflecting optical element). This
results in an increase in resistance to mold release.
The problem with resistance to mold release is not very serious in
the reflecting optical element employed in a conventional scanning
optical device of longer wave length. It has been found out,
however, that, in the reflecting optical element of a device using
a short-wave light source required to ensure a higher degree of
surface precision, the surface roughness affecting the surface
precision of the mirror surface section serving as a reflecting
surface thereby will be deteriorated by the distortion at the time
of mold release. Even if the problem with the contraction of resin
can be solved by hollow molding, a high degree of surface precision
cannot be ensured, as a result.
The object of the present invention is to solve the aforementioned
problem and to provide a resin-made reflecting optical element
characterized by a high degree of mirror surface precision which is
achieved by mitigating the impact of warping and sink marks
resulting from contraction during resin hardening, and by
sufficiently suppressing the distortion of the mirror surface
section caused by mold releasing resistance, or a scanning optical
device using this reflecting optical element.
Means for Solving the Problems
To achieve the aforementioned object, the first embodiment of the
present invention has a longer tabular resin-made substrate having
a hollow portion, and a mirror surface section located at part of
the substrate surface. The hollow portion is located inside the
substrate with the mirror surface section formed thereon, and is
longer than the distance from the center of the mirror surface
section to both ends of the mirror surface section in the direction
of length, and the mirror surface section is a reflecting optical
element wherein the entire mirror surface section protrudes above
the surface of the substrate.
Further, the hollow portion is preferably longer than the distance
from the center of the mirror surface section to both ends of the
mirror surface section in the direction of width.
The reflecting optical element preferably reflects the light
emitted from the light source during the operation of scanning
along the surface of the mirror surface section in the direction of
length.
Further, the surface roughness Ra on the surface of the substrate
with the mirror surface section of the reflecting optical element
formed thereon is preferably formed within the range of Ra.ltoreq.5
(nm).
Another embodiment of the present invention is a scanning optical
device provided with: a light source and polygon mirror; a
converging means for inputting the light emitted from this light
source and converging this light onto the polygon mirror; and a
reflecting optical element for providing f.theta. characteristic to
the light scanned by rotation of the polygon mirror at a prescribed
speed. The aforementioned reflecting optical element includes a
long tabular resin-made substrate provided with a hollow portion
and a mirror surface section located at part of the substrate. The
hollow portion is positioned inside the substrate wherein the
mirror surface section is formed, and is longer than the distance
from the center of the mirror surface section to both ends of the
mirror surface section in the direction of length. The mirror
surface section is characterized in that the entire mirror surface
section protrudes above the surface of the substrate.
Further, the hollow portion of the reflecting optical element used
in the scanning optical device is preferably longer than the
distance from the center of the mirror surface section to both ends
of the mirror surface section in the direction of width.
Further, the surface roughness Ra on the surface of the substrate
with the mirror surface section of the reflecting optical element
used in the reflecting optical device is preferably formed within
the range of Ra.gtoreq.5 (nm).
The wavelength of the light emitted from the light source is
preferably 500 nm or less.
Effects of the Invention
As described above, according to the present invention, there is
provided a resin-made reflecting optical element including a hollow
portion, and this hollow portion is formed inside the substrate to
be longer than the mirror surface section in the direction of
length, namely, in the scanning direction. This structure ensures
that the warping that occurs in the direction of length due to
contraction during resin hardening is mitigated across the entire
mirror surface section. Further, the entire mirror surface section
protrudes above the surface of the substrate. This suppresses an
increase in resistance to mold release that occurs when a mold is
gripped by the resin molded product during contraction of the resin
molded product. Thus, the present invention provides a resin-made
reflecting optical element characterized by the mirror surface
precision higher than that of the conventional element.
Further, use of the reflecting optical element provides a scanning
optical device and image forming device using a blue laser capable
of high definition image recording, at less expensive costs than
the conventional equipment using glass-, metal- or ceramic-made
optical element.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram representing the profile of a
reflecting optical element in a first embodiment of the present
invention, wherein FIG. 1a is a top view of the reflecting optical
element as observed from the direction of depth, while FIG. 1b is a
top view of the reflecting optical element as observed from the
direction of width;
FIG. 2 is a schematic diagram representing the method of molding a
reflecting optical element in a first embodiment of the present
invention, wherein FIG. 2a is a top view of the reflecting optical
element as observed from the direction of depth, while FIG. 2b is a
top view of the reflecting optical element as observed from the
direction of width;
FIG. 3 is a schematic diagram representing the profile of a mold,
wherein FIG. 3a is a cross sectional view being cut by the
perpendicular surface including the bisector in the direction of
width, while FIG. 3b is a cross sectional view being cut by the
perpendicular surface including the bisector in the direction of
length;
FIG. 4 is a functional block diagram showing the injection molding
machine provided with a detecting means;
FIG. 5 is a chart representing the relationship among the
temperature detected by a detecting means, charging of resin, and
filling of compressed gas;
FIG. 6 is a flow chart showing the operations from the step of
filling the mold cavity with resin to the step of removing the
molded product from the mold;
FIG. 7 is a schematic diagram representing the profile of a
reflecting optical element in a variation of the first embodiment
of the present invention, wherein FIG. 7a is a top view of the
reflecting optical element as observed from the direction of depth,
while FIG. 7b is a top view of the reflecting optical element as
observed from the direction of depth; and
FIG. 8 is a perspective view representing the scanning optical
device in a second embodiment of the present invention.
DESCRIPTION OF EMBODIMENTS
Embodiment 1
FIG. 1 is a schematic diagram representing the profile of a
resin-made reflecting optical element having a hollow portion which
is longer in the direction of length than the mirror surface
section, in a first embodiment of the present invention. FIG. 1a is
a top view of the reflecting optical element as observed from the
direction of depth, while FIG. 1b is a top view of the reflecting
optical element as observed from the direction of width.
(Profile of Optical Element)
The resin-made reflecting optical element of the present embodiment
(hereinafter also referred to as "reflecting optical element of the
present embodiment") includes: a long tabular substrate 3; a mirror
surface section 2 positioned on one surface of the substrate 3; and
a hollow portion 4 positioned inside the substrate 3 on the back
surface of the mirror surface of the mirror surface section 2, and
the length of the hollow portion 4 in the direction of length is
greater than that of the mirror surface section 2 in the direction
of length. Further, both ends of the hollow portion 4 are formed
outside the mirror surface section 2 in the direction of length.
This structure ensures that the tensile stress occurring due to
contraction of resin during resin hardening is released to the
hollow portion 4. Thus, the warping caused by resin contraction in
the direction of length is mitigated over the entire mirror surface
section 2, with the result that the surface precision is
enhanced.
The conventional method has problems of gripping of the mold by the
molded product due to the resin contraction, and the distortion of
the mirror surface section 2 that results from resistance to mold
release. These problems can be solved by allowing the mirror
surface section 2 to project from the substrate 3 over the ensure
surface in the direction of depth, thereby mitigating the
distortion of the mirror surface section 2 resulting from
resistance to mold release. Further, the profile of the mirror
surface may be changed by correction of the mirror surface at the
time of manufacturing the optical element (resin molded product),
for example, by cutting the mirror surface section 2 in the
direction of depth. The surface of the mirror surface section 2 may
be embedded into the substrate 3 by correction. In this case, the
length wherein the mirror surface section 2 protrudes from the
substrate 3 in advance can be adjusted in anticipation of the
amount of correction of the mirror surface section 2. This
adjustment allows the surface of the mirror surface section 2 to
project from the surface of the substrate 3 after correction as
well, with the result that gripping of the mold by the molded
product is avoided.
In the reflecting optical element of the present embodiment, assume
that the length of the mirror surface section 2 in the direction of
length is L1; the length in the direction of width is W1; the
length of the hollow portion 4 in the direction of length is L2;
the length in the direction of width is W2; the length in the
direction of depth is D2; the length of the substrate 3 in the
direction of width is W4, and the distance from the end of the
mirror surface section to the end of the substrate with reference
to one side in the direction of length is L5. On this assumption,
the distance L3 from the end of the mirror surface section to the
end of the hollow portion with reference to one side in the
direction of length can be expressed as 0.ltoreq.L3<L5, and the
distance W3 from the end of the mirror surface section to the end
of the hollow portion with reference to one side in the direction
of width can be expressed as 0.ltoreq.W3<W2/2. The structure is
preferably designed to meet these expressions.
The length D1 of the mirror surface section 2 protruding from the
surface of the substrate 3 in the direction of width can be
expressed by 0.1 (mm)<D1<3 (mm). When mold release is taken
into account, the lateral area of the mirror surface section,
hence, resistance to mold release, will be increased, with the
result that the mirror surface precision on the periphery will be
deteriorated. Thus, the expression 0.1 (mm)<D1.ltoreq.0.3 (mm)
is preferably satisfied.
The relationship between the length W1 of the mirror surface
section 2 in the direction of width and the length W2 of the hollow
portion 4 preferably meets the expression
0.01.ltoreq.W2/W4.ltoreq.1.
In FIGS. 1a and 1b, the hollow portion 4 is placed at the center
both in the direction of width and in the direction of depth, and
is illustrated in a straight line in parallel with the mirror
surface section 2. This is meant only for schematic illustration,
without giving any restriction to the profile or positional
relationship of the hollow portion 4.
(Material of Substrate)
The following describes the material of the reflecting optical
element in the present embodiment: The resin material constituting
the substrate of the reflecting optical element is exemplified by
polycarbonate, polyethylene terephthalate, polymethyl methacrylate,
cycloolefin polymer or a resin made of two or more of these
substances. In the reflecting optical element, use of polycarbonate
and cycloolefin polymer is particularly preferred.
(Material of Mirror Surface Section)
The following describes the material constituting the mirror
surface section of the reflecting optical element. Examples of the
material constituting the mirror surface section include silicon
monoxide, silicon dioxide, and alumina, for example. Any commonly
known method such as a vacuum vapor deposition method, sputtering
method or ion plating method can be used to form a film.
(Molding Method)
The following describes a method for molding the reflecting optical
element with reference to FIGS. 2, 4, 3 and 6: FIG. 2 is a
schematic diagram representing the method of molding a reflecting
optical element in the present embodiment. FIG. 4 is a functional
block diagram showing the injection molding machine provided with a
detecting device used in the step of molding in the present
embodiment. FIG. 3 is a schematic diagram representing the profile
of a mold. FIG. 6 is a flow chart showing the operations from the
step of filling the mold cavity with resin to the step of removing
the molded product from the mold.
The injection molding machine used for molding includes a mold 42
equipped with a cavity 31, a charging means 32 for charging the
cavity 31 with resin, a detecting means 33 for detecting the tip
end at the time of resin injection, a gas filling means 34 for
filling compressed gas into the resin having been charged, and a
control means 35 for controlling the start and stop of resin
charging operation, and start and stop of compressed gas filling
operation.
(Mold)
The cavity 31 has an internal surface for forming the first surface
portion 11 and second surface portions 12 constituting the outer
surface of the resin molded article for the optical element.
Referring to FIG. 3, the following describes the profile of the
mold 42. FIG. 3a is a cross sectional view of the mold 42 when cut
by a perpendicular line including a bisector in the direction of
thickness. FIG. 3b is a cross sectional view of the mold 42 when
cut by a perpendicular line including a bisector in the direction
of length between the internal surfaces of the cavity 31 including
a first region 311 for forming the first surface portion 11 and a
second region 312 for forming the second surface portions 12.
In the mold 42 on the side (top surface side) in contact with the
first region 311 and second region 312 of the cavity 31, the
portion corresponding to the first region 311 of the cavity 31 is
provided with a mirror surface forming section 315 as a convex
portion. When the mirror surface forming section 315 is provided,
the mirror surface section 2 is formed in such a way as to protrude
over the first surface 11. Gripping of the mold by the molded
product does not occur, despite hardening and contraction of the
resin molded product (reflecting optical element), so that the
resistance to mold release is mitigated when the mold 42 on the
stop surface side is removed.
Here, to achieve the surface precision used in the short-wave
having a wavelength of 500 nm or less, the mirror surface forming
section 315 is machined to a surface roughness Ra of 5 mm or less.
This surface roughness Ra is preferably in the range of 2 to 3 nm
or less.
Referring to FIG. 4, the mechanism surrounding the mold 42 in an
injection molding machine will be described. A gate 321, runner 322
and spool 323 are formed continuously on the cavity 31. A heater
(not illustrated) is provided along the cavity 31, runner 322 and
spool (passage of the mold) 323. This heater ensures that the
molten resin having contacted the cavity 31 and passage of the mold
will not be solidified by being cooled by thermal conduction and
becoming less fluid. Instead of the heater, a temperature
regulating water channel can be provided on the mold. FIG. 4 shows
the internal surface of the cavity 31 as the outside shape of the
reflecting optical element (resin molded article) 1. FIG. 4 also
shows the gate 321, runner 322 and spool 323 as an outside shape of
the resin passing through them.
(Charging Means)
The charging means 32 is preferably mounted on the mold so that the
resin will be charged from the direction of width of the reflecting
optical element 1 to the direction of length. The nozzle 324 of the
charging means 32 communicates with the spool 323. The charging
means 32 has a screw (not illustrated) for extruding the molten
resin from the nozzle 324. The screw allows the molten resin to be
fed from the nozzle 324 to the spool 323, runner 322 and the gate
321 so that the cavity 31 is filled with resin. The distance
traveled from the screw starting position or the time elapsed after
start of screw traveling corresponds to the amount of the molten
resin to be extruded (injection volume). The volumes of the mold
passage from the spool 323 to the gate 321 and the cross sectional
profile of the cavity 31 at each position in the direction of
length are already known. This makes it possible to calculate the
position of the leading edge of the molten resin charged into the
cavity 31, based on the distance traveled from the screw starting
position or the time elapsed after the start of screw
traveling.
(Detecting Means)
The detecting means 33 is a temperature sensor for detecting the
temperature on the internal surface of the cavity 31. One or more
detecting means 33 including the second region 312 of the internal
surface of the cavity 31 for forming the second surface 12 are
arranged on the internal surface of the cavity 31 including the
bottom surface 313 and double lateral wall surface 314, when the
second region 312 is assumed as a top surface. FIG. 4 indicates a
detecting means 33 arranged on the bottom surface 313 opposed to
the second region 312 (top surface) on the side opposite the second
region 312 on the gate side, with respect to the direction of
length. The detecting means 33 is not restricted to a temperature
sensor if it is a sensor capable of detecting the leading edge of
the resin at the time of injection inside the cavity 31. For
example, an ultrasonic sensor or magnetic sensor can be used.
The detecting means 33 can detect the leading edge of the resin
having reached the second region 312 of the cavity 31. The control
means 35 receives the detected temperature t1 from the detecting
means 33 through the interface 38 as a detection signal. The
control means 35 controls the charging means 32 and stops the resin
charging operation, based on the detected temperature t1 from the
detecting means 33. The control means 35 also controls the gas
filling means 34 to start the compressed gas injection.
By providing the detecting means 33 in a region which is same as
the second region 312 in the direction of length and including the
second region 312, the surface precision of the first surface
portion 11 is not adversely affected by the detecting unit 33.
Further, the leading edge of the resin having reached the second
region 312 and the leading edge of the hollow portion formed inside
the resin are detected directly by the detecting unit 33, and a
stop of the resin charging operation and a start of injection
operation of compressed gas are controlled in response to this
detection signal. Then it becomes possible to elongate the hollow
portion to the second surface 12 certainly.
The control means stores prescribe time in the storage means 36. In
response to the operation having been performed by the operation
means 41, the control means 35 adjusts a prescribed time so that
the updated prescribed time is stored in the storage means 36.
Adjustment of a prescribed time allows the position of the
hesitation mark HM to be adjusted.
(Gas Injecting Means)
The gas filling means 34 includes a tank (not illustrated) for
storing the compressed gas, a solenoid valve 341, and an injection
outlet 342 communicating with the cavity 31. The control means 35
controls the open/close operation of the solenoid valve 341. Any
compressed gas can be used if it does not react or mix with the
resin. For example, an inert gas can be used. When safety and
economy are taken into account, nitrogen is preferably used because
it is non-combustible and non-toxic, and does not require much
cost. The injection outlet 342 is located on the bottom surface 313
of the inner surface which oppose to the second region 312 (top
surface) of the internal surface of the cavity 31. To be more
specific, the injection outlet 342 is provided on the bottom
surface within the space between the positions corresponding to the
end of the first surface and the end of the optical element. The
injection outlet 342 is arranged in the vicinity of the gate and
opened toward the direction of length.
(Storage Means)
The storage means 36 stores the predetermined reference temperature
t0 to be compared with the detected temperature t1 from the
detecting means 33. FIG. 5 shows the detected temperature t1 and
the reference temperature t0.
(Decision Means)
The decision means 37 compares the detected temperature t1 with the
reference temperature t0. If the detected temperature t1 has
exceeded the reference temperature t0, the decision means 37
outputs the result of decision to the control means 35. When the
leading edge of the molten resin has reached the position of the
detecting means 33, the detected temperature t1 detected by the
detecting means 33 is determined as the reference temperature
t0.
(Control Means)
In response to the detected temperature t1 from the detecting means
33, the control means 35 allows the decision means 37 to compare
the detected temperature with the reference temperature. When the
decision means 37 has determined that the detected temperature t1
exceeds the reference temperature t0, the control means controls
the charging means 32 so that charging of the cavity 31 with resin
will be suspended. Further, the control means 35 controls the gas
filling means 34 to start injection of compressed gas into the
charged resin. The control means 35 suspends the inspection of
compressed gas after the elapse of a prescribed time from the start
of injection of the compressed gas. FIG. 6 shows the operation of
stopping the resin charging, and starting the injection of
compressed gas, when the detected temperature t1 has exceeded the
reference temperature t0.
When the compressed gas is filled into the charged resin, the
hollow portion 4 in the resin can be extended in the direction of
length, and formation can reach the second surface 12 along the
first surface 11. This ensures that the hollow portion 4 longer
than the first surface 11 is formed inside the resin in the
direction of length. Thus, the impact of the tensile stress due to
thermal contraction can be released by the hollow portion 4 having
been formed. This reduces warping of the resin molded product.
Further, a hollow portion is formed up to the second surface;
namely, the hollow portion is formed longer than the first surface
11 in the direction of length. This permits the effect of the
hollow portion to work on the entire mirror surface.
Since the compressed gas is injected before resin is cooled
subsequent to suspension of resin charging operation, injection of
the gas is preferably started almost simultaneously with
suspension, or in the range of 1 to 5 seconds after charging with
resin.
Upon receipt of an instruction from the operation means 41, the
control means 35 allows the updated reference temperature t0 to be
stored in the storage means 36. To adjust the time of stopping the
resin changing and starting the compressed gas filling operation,
one has only to adjust the temperature t0. The reference
temperature t0 can be determined empirically by repeating the test
of manufacturing the substrate of the reflecting optical element 1
and by measuring and evaluating the produced reflecting optical
element 1. The reference temperature t0 is determined in relative
terms according to the material of the substrate of the reflecting
optical element 1, temperature of the heating cylinder, and the
amount of resin charged per unit time.
The following describes a series of operations: In the first place,
the control means 35 controls the charging means 32 to rotate the
screw in such a way that molten resin is emitted from the nozzle
324. The resin passes through a spool 323, runner 322 and gate 321,
and is changed into the cavity 31 (Step S101). In this case, the
solenoid valve 341 is closed. Further, the control means 35 has not
yet received a detection signal from the detecting means 33.
The cavity 31 is further charged with molten resin. The tip end of
the molten resin having reached the second surface 12 is detected
by the detecting means 33. When the control means 35 has received
the detection signal of the detecting means 33 (Step S102: Yes),
the control means 35 controls the charging means 32, and suspends
the cavity 31 to be charged with resin (Step S103). Then the
control means 35 controls the gas filling means 34, and releases
the solenoid valve 341. This procedure enables the compressed gas
in a tank (not illustrated) to be jetted into the cavity 31 from
the injection port 342. Since the injection port 342 is arranged on
the bottom surface opposed to the second region 312, and the
injection port 342 is opened in the direction of length, the
charged resin is filled with the compressed gas in the direction of
length (Step S104). This procedure permits a hollow portion to be
formed in the resin in the direction of length.
Then the molten resin is solidified and cooled by the thermal
conduction with the mold. The hollow portion 4 is kept at a
prescribed pressure until the resin is solidified and cooled (Step
S105). If the pressure is maintained at this level, the first
surface 11 is pressed against the first region 311. This enhances
the surface transfer property of the first surface 11.
Then the compressed gas is removed from the hollow portion 4, and
the mold is opened to remove the reflecting optical element (resin
molded product) (Step S106).
In the flow chart illustrated in FIG. 6, when one detecting means
33 is installed on the bottom surface opposed to the second region
312, the control means 35 stops the resin charging operation, and
starts the compressed gas filling operation. The present embodiment
is not restricted thereto. Namely, when a detecting means 33 is
installed on the bottom surface opposed to the second region 312,
make setting in advance to determine whether or not the control
means 35 should control the charging means 32 and gas filling means
34, depending on the ordinal number of a particular detecting means
33 from which the detection signal has been received. This setting
is stored in the storage means 36. In FIG. 6, when the control
means 35 has received a detection signal from a prescribed
detecting means 33 (Step S102: Yes), the control means 35 controls
the charging means 32, and stops the resin charging operation (Step
S103). The control means 35 then controls the gas filling means 34
in such a way as to control the start of compressed gas filling
operation (Step S104).
(Example of Variation)
Referring to FIG. 7, the following describes an example of
variation of the reflecting optical element in the present
embodiment. FIG. 7 is a schematic diagram representing the profile
of a reflecting optical element in an example of variation. FIG. 7a
is a top view of the reflecting optical element as observed from
the direction of depth, while FIG. 7b is a top view of the
reflecting optical element as observed from the direction of width.
The structure is the same as that of the aforementioned reflecting
optical element 1, except for the relationship between the length
W3 of the mirror surface section 6 in the direction of width and
the length W5 of the hollow portion 8. Thus, the following
describes only the differences.
In the aforementioned reflecting optical element 1, the length W1
of the mirror surface section 2 in the direction of width and the
length W2 of the hollow portion 4 meet the relationship of
W1>W2. In the reflecting optical element 5 of the example of
variation, however, the length W6 of the hollow portion 4 is
greater than the length W5 of the mirror surface section 6, and a
relationship of W5<W6 is satisfied. Further, both ends of the
hollow portion 8 are formed outside both ends of the mirror surface
section 6 in the direction of width. This structure mitigates
warping and sink marks resulting from resin contraction, in the
direction of width as well, and enhances surface precision.
The length D5 of the mirror surface section 6 protruding from the
surface of the substrate 7 in the direction of depth is 0.1
(mm)<D5<3 (mm). When mold release is taken into account, the
lateral area of the mirror surface section is increased and the
resistance to mold release is also increased. Thus, the mirror
surface precision in the surrounding area will be deteriorated. To
avoid this, it is preferred that 0.1 (mm)<D5.ltoreq.0.3 (mm)
should be met.
Similarly to the case of FIGS. 1a and 1b, the hollow portion 8 is
located at the center both in the direction of width and in the
direction of depth and is shown in a plane profile in parallel with
the mirror surface section 6 in FIGS. 7a and 7b. It should be noted
that this is only intended to give schematic illustration, with
imposing any restrictions on the profile and positional
relationship of the hollow portion 8.
The reflecting optical element of FIG. 1 or 7 in the present
invention shows the profile of a convex mirror as an Example. It
should be noted that the reflecting optical element is not
restricted to the convex mirror. The present invention is
applicable to the cases especially where a high degree of surface
precision is required in the direction of a prescribed axis, and
the reflecting optical element permits a wide space for the hollow
portion to be assigned from the mirror surface section in the
direction of this axis.
Embodiment 2
FIG. 8 shows an embodiment wherein the reflecting optical element
described in the first embodiment is applied to an f.theta. mirror
in the reflecting type scanning optical device.
FIG. 8 is a perspective view representing a reflecting type
scanning optical device. In FIG. 8, the scanning optical device
includes a light source means 21, condensing means 22 and 24,
polygon mirror 23, plane mirrors 25 and 26, and f.theta. mirror
27.
The light source means 21 includes a laser diode (not illustrated)
and a collimating lens (not illustrated). The laser diode is on-off
controlled according to the image information inputted into a drive
circuit (not illustrated). Laser beam is emitted in the ON mode.
This laser beam is a semiconductor laser of gallium nitride, and
the oscillation wavelength is 408 nm. After having been converged
into approximately parallel beam by the collimating lens, this
laser beam is reflected by the cylindrical mirror as a converging
means 22. The shape of beam is converted into the approximately
straight line wherein the direction of length is parallel to the
main scanning direction, and the beam is led to the polygon mirror
23.
A toric lens as the condensing means 24 has powers different in the
main scanning direction and sub-scanning direction. In the
sub-scanning direction, the laser beam is converged on the scanned
surface. This allows the deflection surface of the polygon mirror
23 and the scanned surface to be kept in the relationship of
conjugation. Thus, the surface inclination error of each deflection
surface of the polygon mirror 23 is corrected by combination with
an extended cylindrical mirror as the aforementioned converging
means 23.
The laser beam having passed the converging means 24 is reflected
by the plane mirrors 25 and 26, and is again reflected by the
f.theta. mirror 27, whereby the laser beam is converged to the
photoreceptor drum 28. The f.theta. mirror 27 corrects the laser
beam deflected at a constant angular velocity in the main scanning
direction by the polygon mirror 23 in such a way that the main
scanning speed on the scanned surface (on the photoreceptor drum
28) is adjusted to a uniform speed. To put it another way,
distortion is corrected.
The photoreceptor drum 28 is driven at a constant speed in the
direction of arrow "b". An image is formed on the photoreceptor
drum 28, based on the main scanning of the laser beam by the
polygon mirror 23 and rotation (sub-scanning) of the photoreceptor
drum 28.
If the reflecting type scanning optical device using an f.theta.
lens is employed as a reflecting optical element, as in the present
embodiment, the main scanning speed can be changed into a uniform
speed without the laser beam passing through the f.theta. mirror.
This makes it possible to avoid the problem of weatherability of
the resin optical element that may occur even when using a
short-wave laser beam such as a blue laser beam, with the result
that high-definition image recording and reproduction can be
achieved.
Further, as described above, the optical surface of the f.theta.
mirror is required to provide a high degree of surface precision
than that required when the f.theta. lens is used. The impact on
the mirror surface section by warping and sink marks during resin
contraction can be mitigated, and a high degree of surface
precision is ensured by using the reflecting optical element of the
present invention, namely, the reflecting optical element which
includes a hollow portion which is longer in the direction of
length than the mirror surface section or long both in the
directions of length and width, and wherein the entire surface of
the mirror surface section is protruding over the surface of the
substrate in the direction of width.
It is to be expressly understood, however, that the scanning
optical device of the present invention is not restricted to the
aforementioned Examples. The present invention can be embodied in a
great number of variations with appropriate modification or
additions, without departing from the technological spirit.
Particularly, the type and arrangement of the optical element used
to form the optical path can be selected as desired. Further, the
reflecting optical element of the present invention is not
restricted to the aforementioned Example, namely, f.theta. mirror.
The present invention can be applied especially to a reflecting
optical element wherein a high degree of surface precision is
required in the direction of a prescribed axis and a wider hollow
portion can be assigned from the mirror surface section.
EXAMPLES
The following describes the present invention with reference to
preferred Examples. In the Example and Comparative Example, the
f.theta. mirror 27 of the reflection type scanning optical device
described with reference to the second embodiment is used as the
resin-made reflecting optical element.
The f.theta. mirror 27 to be manufactured has the following
dimensions: The overall length in the direction of length is 122
mm, the overall width in the direction of width is 20 mm, the
overall width is 5 mm, the length of the mirror surface section is
100 mm, and the width of the mirror surface section is 14 mm. The
resin molded product wherein the mirror surface section is formed
is set to such conditions (resin temperature, mold temperature,
injection speed, injection switch-over position, weighing position,
holding pressure, holding pressure time, gas pressure, gas pressure
time, gas nozzle temperature, etc.) that the surface roughness of
the portion wherein the mirror surface section of the hollow
portion is formed will be 5 nm or less, and the length of the
hollow portion will be 100 nm or more without exceeding 122 mm
corresponding to the length in the direction of length of the
substrate wherein the mirror surface section is formed. After the
molding die is cut and processed as shown in FIG. 3, a hollow
portion is formed.
The resin molded product produced in the aforementioned procedure
was checked to see that the length of the hollow portion in the
direction of length was greater than the length of the substrate in
the direction of length, and the surface precision of the substrate
wherein the mirror surface section of the resin molded product was
measured. As a result, it was possible to manufacture a resin
molded product characterized by a high degree of surface precision
wherein there was little impact of distortion caused by the
resistance to mold release from the molding die and the surface
roughness was 5 nm or less, in conformance to the conditions at the
time of molding. Thus, a reflecting optical element characterized
by surface precision on the same level was produced.
Comparative Example
Unlike the Example, molding operation was performed using the
molding die shown in FIG. 3, under the same conditions as those of
the Example, except for the molding conditions wherein the length
of the hollow portion in the direction of length is smaller than
the length of the substrate in the direction of length. In the
produced resin molded product, the length of the hollow portion in
the direction of length was shorter than the length of the
substrate in the direction of length in conformance to the molding
conditions. However, the surface precision of the resin molded
product was measured to find out that the surface roughness was
greater than 5 nm. It was not possible to manufacture a reflecting
optical element of high surface precision.
DESCRIPTION OF REFERENCE NUMERALS
1 Reflecting optical element 2 Mirror surface section 3 Substrate 4
Hollow portion 11 First surface 12 Second surface 21 Light source
means 23 Polygon mirror 27 f.theta. mirror 28 Photoreceptor drum
(surface to be scanned) 31 Cavity 32 Charging means 33 Detecting
means 34 Gas filling means 35 Control means 36 Storage means 37
Decision means 38 Interface 41 Operation means 311 First region 312
Second region 315 Mirror surface section 341 Solenoid valve 342
Injection port
* * * * *